1. Field of the Invention
The present invention relates to a spread illuminating apparatus as an illuminating means for signboards, various kinds of reflection-type displays and so on, in particular, as an illuminating means for a liquid crystal display.
2. Related Art
As an auxiliary illuminating apparatus for illuminating a screen of a reflection-type liquid crystal display uniformly, the present inventors proposed the spread illuminating apparatus (patent application Ser. No. 182076/98), an outline of which will be explained hereinafter with reference to FIG. 4. This illuminating apparatus 1 is disclosed as a prior art. The spread illuminating apparatus 1 is disposed to cover a screen F (front surface) of a reflection-type liquid crystal display element L. The apparatus comprises a plate-like transparent substrate 2 rectangular in section and made of a highly light permeable material, and a light source portion 4 provided close to one end surface 3 of the transparent substrate 2. The transparent substrate 2 may be wedge-shaped for reducing its weight. Here, in FIG. 4, one surface of the transparent substrate 2 abutting on the reflection-type liquid crystal element L will be denoted as a lower surface 5 and a viewing surface (screen) on the opposite surface as an upper surface (front surface) 6.
As shown in FIG. 5, the light source portion 4 is formed with a bar-like light conductive member 7 and spot-like light sources 9 such as light emitting diodes provided to both ends 8 of the light conductive member 7. An optical path conversion means 11 to be explained later in details is formed on one surface of the light conductive member 7, whose longitudinal surfaces except the one opposing the transparent substrate 2 are covered with a light reflection member (reflector) 12 in order to introduce light beams traveling through the light conductive member 7 into the transparent substrate 2 in a high degree of efficiency.
The optical path conversion means 11 is formed on a surface 14 opposite to a surface 13 facing the end surface 3 of the transparent substrate 2, and comprises a light dispersion portion 15 (black portion in FIG. 5) with a partial coarsening work to form a minutely rugged portion and a plane portion 16 without the coarsening work. Since light beams reflected by the light dispersion portion 15 exit out the surface 13 and enter the transparent substrate 2 in a larger amount than those by the plane portion 16 due to the formation of the minutely rugged portion, the light dispersion portion 15 is so formed as to increase its area as it gets away from the spot-like light source 9.
Thus, the optical path conversion means 11 is formed in consideration of a balance between the distance from the spot-like light source 9 and the area of the light dispersion portion 15, whereby the light beams are uniformly emitted from the surface 13 facing the end surface 3 of the transparent substrate 2 in spite of the fact that the spot-like light source 9 is provided to the end portion 8 of the light conductive member 7, so the light source portion 4 formed with the spot-like light source 9 and the light conductive member 7 functions similar to a fluorescent lamp (cold cathode fluorescent and hot cathode fluorescent lamps, etc.) as a bar-like light source.
And, a light reflection pattern 17 is formed on the upper surface 6 of the transparent substrate 2. The light reflection pattern 17 is constituted with a number of grooves 18 approximately triangular in section and plane portions 19 adjacent to the grooves 18 formed along the end surface 3. The light reflection pattern 17 is formed so that the interval between the grooves 18 varies from spot to spot in order to achieve a uniform emitting of spread illumination from the transparent substrate 2 independent of the distance from the light source 4. That is, the ratio of the width (occupied area) of the groove 18 to the width (occupied area) of the plane portion 19 is set to gradually increase as the groove 18 gets away from the end surface 3 of the transparent substrate 2. For reference, since the grooves 18 of the light reflection pattern 17 formed on the transparent substrate 2 are quite minute, they cannot be visually recognized when viewing a screen.
When such a spread illuminating apparatus 1 is disposed in such a manner as to cover the upper surface of the reflection-type liquid crystal element L, the light beams emitted from the light source portion 4 enter the transparent substrate 2 from the end surface 3, and travel toward the opposite surface 10 as they repeat reflection and refraction therein. Meanwhile, the light beams emitted from the lower surface 5 of the transparent substrate 2 illuminate the reflection-type liquid crystal element L, thereby brightening the screen. Since the amount of light emitted from the lower surface 5 is approximately uniform independent of the distance from the light source portion 4 due to the formation of the light reflection pattern 17, the reflection-type liquid crystal element L can be illuminated in a spread manner.
And, although the spot-like light source 9 is provided to both ends 8,8 of the light conductive member 7 respectively in FIGS. 4 and 5, it may be provided to either one end 8. Moreover, the above discussed optical path conversion means 11 formed on the light conductive member 7 is constituted with a light dispersion portion 15 consisting of a minutely rugged surface and a plane portion 16, but it can be alternately constituted with a portion coated with material containing light dispersion substance and a portion without such a coating, or with a portion with a groove whose reflection angle is set to make reflected light beams enter the transparent substrate 2 and a portion without such a groove.
Now, since the light source portion 4 of the spread illuminating apparatus 1 is formed with the light conductive member 7 and the spot-like light source 9, there has been such a problem as mentioned below. That is, when viewing the screen on the above described spread illuminating apparatus 1 disposed to cover the viewing surface F of the liquid crystal display L, it was found that a stripe pattern of brightness and darkness can be generated orthogonally to the end surface 3, which prevents a uniform spread emitting, causing difficulty in viewing the screen.
This stripe pattern of brightness and darkness was found to be caused by the optical path conversion means 11 provided on the light conductive member 7. That is, while most of the light beams reflected on the light dispersion portion 15 of the optical conversion means 11 exit out the surface 13 and travel into the transparent substrate 2, most of the light beams reflected on the plane portion 16 do not exit out the surface 13 due to a total reflection, so, depending on the condition settled in the light reflection pattern consisting of the light dispersion portion 15 and the plane portion 16, the brightness of the light emitted from the surface 13 becomes uneven. In this case, since the brightness of the light beams entering the transparent substrate 2 is not uniform, the stripe pattern of brightness and darkness orthogonal to the end surface 3 is generated on the screen.
The present invention has been made in the light of the above problem, and an object thereof is to make uniform the brightness of the light beams entering the transparent substrate for achieving a uniform spread illumination in a spread illuminating apparatus.
In order to solve the above problem, according to a first aspect of the present invention, in a side light type of a spread illuminating apparatus in which a bar-like light source is provided close to an end surface of a transparent substrate made of light permeable material, the bar-like light source is formed with a light conductive member made of the light permeable material provided close to and along at least one end surface of the transparent substrate, and a spot-like light source provided to at least one end of the light conductive member, and an optical path conversion means formed with grooves having an identical depth and spaced as closely as workability can allow is provided at least on a surface of the light conductive member opposite to the surface facing the transparent substrate.
In the present invention, since the optical path conversion means of the light conductive member is formed with a light dispersion portion consisting of the grooves having the identical depth and being disposed at a smallest spacing machining can allow, the light beams emitted from the spot-like light source are refracted at the light dispersion portion, and when the light enters the transparent substrate, the brightness of the light is made uniform to the extent that the brightness cannot be visually recognized as uneven. And, the generation of the stripe pattern of brightness and darkness on the screen illuminated through the transparent substrate due to the light reflection at the light dispersion portion is prevented.
Further, according to a second aspect of the present invention, a spacing of the light dispersion portion of the optical path conversion means is set between 0.01 mm to 0.2 mm, which enables the light dispersion portion of the optical path conversion means to have a spacing small enough to prevent generating the stripe pattern of the brightness and darkness and which also allows for the machinability.
Further, according to a third aspect of the present invention, the spacing between the light dispersion portions of the optical path conversion means is set smaller at a farther spot from the spot-like light source. By this invention, the lowering of the brightness due to getting away from the spot-like light source is supplemented by increasing the number of the light dispersion portions per unit of length of the light conductive member to make the brightness uniform everywhere on the light conductive member.
Further, according to a fourth aspect of the present invention, the spot-like light sources are provided to both ends of the light conductive member and the spacing between the light dispersion portions of the optical path conversion means is set smallest at the central portion and is gradually widened toward both ends.
By this structure, since the spot-like light source is provided to both ends of the light conductive member, the brightness of the light conductive member becomes lowest at the center thereof. Therefore, the number of the light dispersion portions per unit of length of the light conductive member is increased as approaching the central portion, whereby the lowering of the brightness due to getting away from the spot-like light source is supplemented to obtain a uniform brightness everywhere on the whole light conductive member. Now, according to this structure, the brightness of the light conductive member is increased as a whole, so the generation of the stripe pattern of the brightness and darkness on the surface to be illuminated through the transparent substrate due to the light reflection at the light dispersion portion is prevented, and the brightness of the spread illuminating apparatus as a whole is increased.
Further, according to a fifth aspect of the present invention, the length of the light conductive member per spot-like light source is set to 30 mm or less. By this constitution, the remarkable lowering of the brightness due to getting away from the spot-like light source is prevented.